Erythromycins are macrolide antibiotics, glycosylated polyketides originally discovered in 1952 in the metabolic products of a strain of Streptomyces erythreus, now classified as Saccharopolyspora erythraea. The antibiotic occurs in various forms, designated A, B, C, and D. Since their discovery, many have worked to prepare derivatives of the molecule to improve or modify its properties. The focus of much of this work involved chemical modification of the naturally produced erythromycin molecule. For example, clarithromycin is a semi-synthetic antibiotic that is made by chemically methylating the hydroxyl group at C-6.
XYZerythromycin AOHOHOMeerythromycin BHOHOMeerythromycin COHOHOHerythromycin DHHOHclarithromycinOHOMeOMe
Azalides, such as azithromycin, are erythromycin derivatives where the C-9 ketone has been replaced with a N—CH2 unit through a Beckmann rearrangement. See, for example, O'Connell et al., “Azalides and methods of making same,” U.S. Pat. No. 6,270,768, incorporated herein by reference.
Ketolides are erythromycin derivatives where the C-3 cladinose sugar is chemically removed and the resulting free hydroxyl group converted into a keto group. For example, Phan et al., “2-Halo-6-O-substituted ketolide derivatives,” U.S. Pat. No. 6,124,269 describes ketolides with a cyclic carbamate group at C-11 and C-12 and an O-alkylaryl group at C-6. Agouridas et al., “Erythromycin compounds,” U.S. Pat. No. 5,635,485 also describes ketolides with a cyclic carbamate group at C-11 and C-12 but which have a -OMe group at C-6 and an alkylaryl group at the carbamate nitrogen.
The complexity of the macrolide molecule has limited medicinal chemistry efforts to produce derivatives of the naturally occurring erythromycins and their precursors. Recently, the discovery and isolation of modular polyketide synthases (“PKS's”) have expanded the scope of macrolide structures that may be made. PKS's are multifunctional enzymes that catalyze the formation of the polyketide chains through repeated reactions between acylthioesters.
The Sac. erythraea PKS, known as 6-deoxyerythronolide B synthase (DEBS), is an assembly of three multifunctional proteins encoded by the eryAI, eryAII, and eryAIII genes and is described in Katz et al., “Recombinant DNA method for producing erythromycin analogs,” U.S. Pat. No. 5,824,513; Katz et al., “Method of directing biosynthesis of specific polyketides,” U.S. Pat. No. 6,004,787; Katz et al., “Polyketide derivatives and recombinant methods for making same,” U.S. Pat. Nos. 6,060,234, 6,063,561, and 6,200,813; each of which is incorporated herein by reference. DEBS produces the polyketide macrolactone 6-deoxyerythronolide B, which is processed by additional tailoring enzymes present in Sac. erythraea to make erythromycins A-D. The collective assembly of the PKS gene and the genes for the tailoring enzymes are referred to as the biosynthetic gene cluster. The organization of the gene cluster is described in Summers et al., “Polyketide-associated sugar biosynthesis genes,” U.S. Pat. No. 5,998,194, incorporated herein by reference.
Recombinant methods using vectors encoding a variety of PKS's, including the PKS from Sac. erythraea, to make novel polyketides are described in Khosla et al., “Recombinant production of novel polyketides,” U.S. Pat. Nos. 5,672,491, 5,830,750, 5,962,290, 6,022,731, and 6,077,696; Khosla et al., “Recombinant combinatorial genetic library for the production of novel polyketides,” U.S. Pat. No. 5,712,146; Khosla et al., “Method to produce novel polyketides,” U.S. Pat. Nos. 6,066,721, 6,221,641, and 6,261,816; Barr et al., “Production of polyketides in bacteria and yeast,” U.S. Pat. Nos. 6,033,883 and 6,258,566 and PCT publication WO 98/27203; Khosla et al., “Biosynthesis of polyketide synthase substrates,” PCT publication WO 01/27305; and Santi et al., “Heterologous production of polyketides,” PCT publication WO 01/31035; each of which is incorporated herein by reference. Leadlay et al., “Erythromycins and process for their preparation, “U.S. Pat. No. 6,271,255, incorporated herein by reference, describes additional methods for modifying the loading domain and thus varying the nature of the starter units that initiate polyketide synthesis. Methods for making polyketides in a cell-free system are described, for example by Khosla et al., “Synthesis of polyketides from diketides,” U.S. Pat. No. 6,080,555; Khosla et al., “Cell-free synthesis of polyketides,” U.S. Pat. No. 6,274,560, and PCT Publication No. WO 97/02358, each of which is incorporated herein by reference. Erythromycin analogues where the naturally occurring ethyl group at C-13 is replaced with other groups have been described, for example in Dirlam et al., “Novel macrolides,” PCT publication WO 99/35156; Jin, “Novel erythromycin derivatives,” PCT publication WO 99/35157; Ashley et al., “Synthesis of oligoketides,” U.S. Pat. No. 6,492,562; McMillen & Kaneko, “Ketolide antibiotics,” PCT publication WO 00/44761; Grant et al., “Ketolide antibacterials,” PCT publication WO 00/62783; and Chu, “Anti-infective compounds,” U.S. Pat. Nos. 6,395,710 and 6,451,768 and PCT publication WO 01/49699; and Xue et al., “Multi-plasmid approach to preparing large libraries of polyketides,” PCT publication WO 00/63361; each of which is incorporated herein by reference.
Various macrolides are also disclosed in U.S. Pat. Nos. 6,451,768 and 6,395,710 both of which are incorporated herein by reference in their entirety and for all purposes. U.S. Pat. No. 6,492,562, also herein incorporated by reference in its entirety for all purposes, describes methods for preparing various macrolides.
Due to the increase in the incidence of resistant strains to currently used antibiotics, a need exists for novel compounds having antibiotic activity, particularly against resistant strains. The present invention fulfills this need by providing novel erythromycins, ketolides, and azalides.